Method for centrifuging and washing sugar massecuites and similar mixtures



Dec. 3, 1940. ROBERTS AL 2223,66?)

.METHOD FOR CENTRIFUGING AND WASHING SUGAR MASSECUITES AND SIMILARMIXTURES Filed Sept. 29, 1959 IINVENTORS 42 EUGENE ROBERTS GEORGE E.STEVENS 7 a l e M ATTORNEYS Patented Dec. 3, 1940 UNITED STATES PATENTOFFICE METHOD FOR CENTRIFUGING AND WASH- ING SUGAR. MASSECUITES ANDSIMILAR MIXTURES Eugene Roberts; Hastings, N. Y., and George E. Stevens,Denver, Colo., assignors to The Western States Machine Company, NewYork, N. Y., a

corporation of Utah Application September 29, 1939, Serial No. 297,086

7 Claims.

By the us'e of the present improvements the amount of washing liquid andthe dissolution of crystals may be substantially reduced, the durationof a centrifugal cycle may be shortened, and the quality'of the washedcrystalline product may be improved.

Various processes have been used for washing the wall of sugar in acentrifugal in order to remove adherent syrup remaining on the crystalsafter the preliminary purging stage. In some factories the washing hasbeen done with steam; in others, a spray of warm water (e. g., F.) hasbeen delivered onto the sugar. The use of steam for washing has beenattended by inferior results because of its poor penetration of thesugar wall, its retarded action and its characteristic of over-treatingthe inside of the sugar wall and dissolving too much grain before theaverage purity of the sugar can be brought to a satisfactory point. Theuse of warm water also has failed to give the desired results. In recentyears an improved andmore emcient practice has been provided whichinvolves the application of a fine hot water spray to the sugar byforcing hot. water to 209 F.) through a spray nozzle under considerablepressure (e. g., about 30 lbs. per square inch). I

This more recent method'of .washing has given results superior to thoseof earlier methods, par ticularly whe carried out after the centrifugalhas been ace; rated to a very high speed, but it has still been oossibleto wash the crystals of a very fine grained or smeared massecuite-to asatisfactory purity without employing noticeably large quantities ofwater and dissolving large amounts of the sugar crystals, and difficultyhas been encountered in purging, washing and drying the sugar crystalsof such massecuite s to a satisfactory moisture content without alsoprolonging the centrifugal cycle objectionably.

A further problem is encountered in the treatment of fine-grained or"smeared crystallizer massecuite, in that certain massecuites of thistype tend to form a tough skin of molasses on the inside of the sugarwall during the purging stage of the centrifuging cycle. This skin notonly prevents proper purging of the mother liquor from the sugar butalso prohibits efilcient washing countered in the drying of very finegrained massecuites during centrifugal treatment may be traced to localcooling of the inside portion of the charge in the revolving centrifugalbasket, and that this local cooling to a large extent limits theefiectiveness of existing washing methods in the treatment of variousother types. of massecuites and magmas. When the charge is introducedinto the centrifugal basket, according to proper practice, it ispreferably at a comparatively high temperature and has a viscosity atsuch temperature which might be expected to enable optimum washing anddrying results. ing the acceleration of the centrifugal, however,strongair currents develop inside the basket and cause a'substantialtemperature reduction. Although the average temperature of the chargemay not be greatly reduced, pronounced cooling occurs near the insideface of the sugar wall.

Local cooling and congealing of syrup, in the case of certain smearedcrystallizer massecuites (where fine crystals tend to fill the voidsbetween coarser crystals), sometimes prevent some of the mother liquorfrom passing through the inner portion of the sugar wall, and this isbelieved to account for the formation of the tough "skin mentionedhereinabove. Under such conditions it has not been possible to wash thecharge in the centrifugal until the skin has been removed or otherwiseeliminated.

In these and other cases, the application of a fine hot water spray tothe charge during the latter part of, or after, the acceleration stageof the centrifugal cycle, even at spray nozzle tein= perature of 170 to200 F., has been found. sufilclent to produce optimum centrifugingresults, especially when treating mixtures con taining veryfinecrystals. The hot water spray is so reduced in temperature, eitherby air circulation inside the centrifugal basket or by contact with thecooled inside portion of the sugar wall, or by both, that anobjectionable quantity of washing liquid is often required to carryaway. the adherent syrup and bring the sugar crystals to the desiredpurity, and when the required Dur-.

quantities of water are used the sugar wall is not heretoforeencountered may be avoided, and that the centrifuging and washing ofmamecuites and magmas, or of other mixtures of crystalline ma terials intheir ,niother liquor, can be carried but with increased ,efliciency byapplying to the charge in the centrifugal, while the basket is revolvingat high speed, a very hot mist consisting of both liquid and steam at aspray nozzle temperature substantially above 212 F. The application of awashing agent of this type, which is forced through the spray nozzleunder elevated pressures, permits a large volume of liquid to reach andpass uniformly through the sugar wall in a comparatively short intervalof time,- and the temperature of the mist as it strikes the inside faceof the sugar wall remains high enough, notwithstanding the coolinginfluence of 'air currents in the basket at high centrifugal speeds, toraise the temperature of locally cooled areas and largely to cure theirtendency to prevent efflcient washing and drying of the crystals in thebasket. This effect, together with the very rapid and uniform passage ofthe washing agent through the charge, permits the washing operation tobe carried out with much less washing agent than heretofore, and theamount of sugar dissolved by the washing operation is substantiallyreduced. The washed sugar Wall is hotter, cleaner and more pervious, sothat the drying stage of the centrifugal cycle requires less time inorder to produce a product of the desired low moisture content.Furthermore, the sugar discharged from the centrifugal may be of higherquality and is less eroded by the washing agent. In the case of white orrefined sugar still another advantage is realized in that thetemperature of the sugar is higher when discharged, so that the finaldrying process may be facilitated.

When the method herein disclosed is used in the centrifuging ofskin-forming crystallizer massecuites, the washing of the charge by themist of superheated liquid and steam results in immediate melting of theskin and purging thereof through the sugar wall. No mechanical removalof the skin is necessary; yet the centrifugal cycle proceeds withoutdelay, andthe sugar may be washed to a. high puritywith only a smallquantity of washing agent. g

We have discovered, contrary to expectations based on prior-experiencewith steam as az-washing agent, that an exceedingly eflicient cleansingaction is obtained by the use of the present method and that the sugarcrystals are not damaged by the hot mist at spray nozzle temperatures ashigh as 250 F. The actual temperature to be employed may be varied, forexample, ac-

. cording to the type of mixture being treated, the

atmospheric temperature conditions at the centrifugals, and the natureof the centrifuging operations. The temperature of the washing agent,however, should not be raised substantially above 250 F., as the liquidcomponent at such temperatures becomes essentially a vapor and does notpossess sufflcient body for an efficient washing action.

It is advantageous to cover the top or bottom opening of the curb, orboth openings, after the basket has been loaded, so that the harmfuleffect of cooling air currents may be reduced during the spinning of thecentrifugal, and so that the hot mist may be confinedduring thewashingstage of the cycle.

In a preferred example of the practice of the present invention, acharge of the massecuite or other mixture to be centrifuged isintroduced into the centrifugal basket, the opening in the curb top iscovered, the basket and charge are accelerated to ahigh speed in suchmanner as to purge most of the syrup from the crystals, and

after the acceleration stage the wall of material remaining in therapidly revolving basket is washed with a very hot mist of superheatedwater and steam, which is delivered through a spray nozzle at a finaltemperature of about 225 to 235 F. and under elevated pressure of about30 to 50 lbs. per square inch.

While the most, satisfactory liquidcomponent of the washing mixture iswater, we also contemplate that clear sugar solutions may be used undersome conditions.

The mist of hot water and steam used as the washing agent is preferablyproduced as follows: A supply of hot water is provided at'a temperaturebetween about and 200 F. and under pressure of about 20 to '70 lbs. persquare inch. A separate supply of saturated steam is provided underpressure of about 20 to 70 lbs. per square inch, the steam pressurepreferably being approximately the same as the water pressure. When awashing operation is to be carried out, the steam and hot water areadmitted together into a common chamber, where co-mingling oc-' ours,and from this chamber the resulting mixture, at a temperature initiallyonly slightly higher than the water temperature but progres-' sivelyincreasing to a temperature as high as 250 F., passes througha pipe intothe-spray nozzle ofthe centrifugal, from which a mist of superheatedwater and steam is delivered onto the wall of material inthecentr-ifugal basket. H

These ranges of. temperatures and pressures are not intended aslimitations, except as may be required by the appended claims, but theyrepresent approximate boundaries of the most efficient practicaloperations. In our usual practice the temperature. of the water-steammixture entering the spray nozzle is recorded at about 225 to 235 F. inthe latter part of the washing stage. The pressure at the spray nozzleis usually about 30 to 50 lbs. per square inch, but this factor issubject to rather wide variation, depending on the steam and waterpressures, the size of the nozzle orifices and the desired rate ofapplying the washing mixture.

The operation of this embodiment is characterized by the fact that therate of flow of washing water, that is, the body and cleansing action ofthe washing medium, is comparatively large in the initial part of thewashing stage, which conforms to the need for removing substantialamounts of adherent syrup from the.

crystals, and as the washing proceeds a smaller quantity of water and alarger quantity of steam are applied to the charge, at a highertemperature, which has the effect of increasing thetemperature of thecrystals and improving their drying qualities so that the drying stageof the cycle is carried out more efficiently.

As an alternative but somewhat less desirable procedure, due primarilyto the need for more expensive equipment, a supply of superheated watermay be provided and maintained under pressure for admission to the spraynozzle during the washing stage of the centrifugal cycle. A hot mist ofwater and steam is produced from the nozzle and sprayed onto the chargein 'the basket when the pressure is released. In this embodiment of themethod, the water is preferably held at a temperature of about 225 to250 F.

The accompanying drawing illustrates a new arrangement of apparatuswhich we have provided for carrying out a preferred embodiment of thepresent invention. In the drawing:

- controlled by a valve 32.

Figure 1 is an elevation, partly diagrammatic, illustrating part of acentrifugal machine equipped with means for practicing the improvedmethod;'

Figure 2 is a plan view of the centrifugal curb top, showing a suitableconstruction of curb 'top cover for use in excluding cool air from thecharge during the spinningcycle; and

Figure 3 is a cross section showing details of the mixing unit whichco-mlngles the hot water and steam during their passage to the spraynozzle.

Referring to the drawing for illustrative details-Figure 1 shows partsof a high speedsugar centrifugal, including a perforate basket l0,suspended on a spindle l2, and a surroundin curb 14 having a curb top I6with a central opening 18 and a. curb bottom 20 with a central open-(not shown) is provided under pressure for admission to a steam line 34,controlled by avalve Means are provided, conveniently on the curb topii, for combining the steam and hot water to form a very hot mixturesuitable for delivery through the spray nozzle 24. In the illustratedform (see Figure 2) this means includes an elongated chamber 40 which isreduced in diameter at its forward end and there connected with a pipe42 leading to the spray nozzle. The water line 30 is connected withchamber 40 near its back end, preferably 'so that the water enters inradial direction. The steam line 34 is connected with an injector 44,which projects axially into the chamber to a point beyond the waterinlet. It is therefore apparent that, when valves 32 and 36 are open,hot water is forced through chamber 40 from pipe 30 and steam is forcedthrough chamber 40 from pipe 34 and injector 44. The resulting mixturepasses onward through pipe 42 and nozzle 24, and from the latter a veryhot mist of water and steam is delivered onto the charge in the basketI0. v

A cover 50 is preferably provided on the curb top l6 for closing theopening I 8 during the spinning cycle. While either the top opening l8or the bottom, opening 22, or both, may be covered to advantage, the useof only a top cover gives satisfactory results and is more convenientthan other arrangements.

The curb top cover 50 (see Figure 3) includes two dissimilar sector-likesections 52 and 54, which are swivelled to the curb top from links 56and 58, respectively. A connecting link 60 causes the two sections tomove together. A handle 62 is provided on section 52 to facilitatemovement of the cover to and from closed position. The curb top I 6 hasan integral sectorlike section I! which projects toward the spindle l2and through whichextends the spray nozzle pipe. When the cover is closedthe entire opening I8 is covered, with the exception of a small spacearound the spindle to allow swaying movement of the latter. Under suchconditionsthe A supply of steam objectionable cooling influence of aircurrents inside the revolving basket is'somewhat reducedp The positionsassumed by the cover sections when the cover is open are indicated bythe broken lines in Figure 3.

It is obvious, of course, that other types of curb top covers may beemployed, and also that the use of a cover is unnecessary, althoughadvantageous. The preferred type of cover herein mentioned is disclosedand claimed in a copending application of Walter Hoffman, Serial No.202,900, filed April 19, '1938.

In addition to the foregoing equipment, the apparatus is provided withmeans for simultaneously opening the valves 32 and 36. While variousmeans may be used for this purpose, the valves may have stems l and I2,respectively, which are spring-held in closed position.- A control shaft14 may be arranged withfingers 16 and 18 which cooperate with the stemsl0 and 12, respectively. When shaft 14 is turned the fingers lift thevalve stems against spring tension and open both valves at the sametime. The turning of shaft 14 may be efiected manually, for ex-- ample,by a lever 80, or by automatic time-controlled means such as heretoforeinvented by Eugene Roberts and now well known in the art.

Means also may be provided for opening the steam valve 36 independent ofthe water valve 32, as in some cases the admission of steam into thecentrifugal basket before or after the washing stage of the cycle mayresult in some advantage. For this purpose the finger 18 may be movableindependently, by means of a lever 82.

It is desirable that the apparatus be provided with instruments forindicating temperature and pressure conditions, so that departures fromdesired practice may be observed and corrected. A

pressure gauge 90 may be connected with pipe 42 to indicate the pressureof the steam-water mixture entering the spray nozzle. A temperaturerecorder 92 may be provided, with its bulb located near the entrance tothe nozzle, as at 93, to record the temperatures of the washing mixture.In addition, another pressure gauge 94 may be connected with the steamline 34, and another temperature recorder 96 may be connected with thehot water line 30.

Theme of the present invention in the centrifuging of extremelyfine-grained white massecuites, as compared with the best priorpractice, permits an increase of centrifugal capacity, by shortening thecycle, of from 8to 20%, permits the amount of wash water to be reducedfrom 25 to 40%, with a proportionate reduction in the dissolution ofsugar crystals, and produces centrifuged sugar of lower moisturecontent. Improvements of similar'extent are obtained in the treatment ofother types of massecuites and magmas.

The improved method and apparatus herein disclosed and claimed areparticularly useful for carrying out centrifugal washing operations inprocesses such as disclosed in the following pending applications:Eugene Roberts, Serial No. 113,542, filed December 1, 1936; EugeneRoberts, Serial No. 140,092, filed May 1, 1937; and George E. Stevens,Serial No. 151,772, filed July 3, 1937.

While we have described and illustrated numercontribution to the art, asintended to be set forth in the appended claims.

We claim:

1. The method of centrifuging mixtures consisting of crystals in theirmother liquor which comprises introducing a charge of the mixture into acentrifugal basket, spinning the basket and charge to purge motherliquor from the crystals, and washing the charge while it is spinningwith a hot mist consisting of superheated aqueous liquid and steam.

2. The method of centrifuging mixtures of sugar crystals and syrup whichcomprises introducing a charge of the mixture into a centrifugal basket,spinning the basket and charge to purge syrup'from the crystals, andwashing the charge while it is spinning with a hot mist consisting ofsuperheated water and steam.

3. The method of centrifuging mixtures of sugar crystals and syrup whichcomprises introducing a charge of the mixture into-a centrifugal basket,accelerating the basket and charge substantially to maximum speed topurge most of the syrup from the crystals, and thereafter washing thecharge while it-is spinning at high speed with a hot mist consisting ofsuperheated water and steam. I

4. The method of centrifuging mixtures of -sugar crystals and syrupwhich comprises introducing a charge of the mixture into a centrifugalbasket, spinning the basket and charge to purge syrup from the crystalsand spraying onto the charge while. it is spinning, from a spray nozzlelocated inside the basket, a watery mist consisting of superheated waterand steam at a nozing hot mist of water and steam through a spray nozzleand onto the charge in the basket.

6. The method of washing syrup from sugar crystals in a revolvingcentrifugal basket which comprises providing a supply of hot water at'a, temperature between 160 and 200 F. and under pressure of between 20and 70 lbs. per square inch, providing a separate supply of saturatedsteam under pressure of between 20 and 70 lbs. per square inch, leadingstreams of said water and steam together and co-mingling the same andspraying the resulting hot mist of superheated water and steam onto thecharge in the basket.

'7. The method of washing syrup from sugar crystals in a revolvingcentrifugal basket which comprises providing a supplyof superheatedwater under pressure at a temperature between about 225 and 250 F.,releasing the pressure and leading the water to a spray nozzle locatedinside therevolving basket, and spraying ontov the charge in the basketa resulting hot mist of superheated water and steam.

EUGENE ROBERTS. GEORGE E. STEVENS.

